Perillyl alcohol is one of two monoterpines under development for possible clinical use as an anticancer agent. Monoterpines are a class of compounds produced by plants which appear to have multiple cellular effects. One of the most studied effects and a possible mechanism for the observed antitumor effect is inhibition of protein isoprenylation. The antitumor effect of monoterpines has been shown in vitro and in vivo primarily against mammary carcinoma.